Rail crossings and turnouts are points where two sets of track cross. The center part of the crossing is sometimes referred to as a frog. Frogs can be cast or fabricated. For heavy use, frogs are sometimes formed from a durable steel such as manganese to increase resistance to wear and impact. Manganese frogs are a standard part of the mining, tunneling and railroad industry.
The rails connecting the switch rails to the frog are called closure rails. A frog has a toe end connected to the closure rail and a heel end at the end of a frog furthest from the switch. The frog point is the area where the running edges of two crossing rails come together. The frog has wing rails, which are two small rails at the heel end of the frog running essentially parallel to the wheel path along each side of the frog point. The wing rails support the wheel of the train car as the wheel crosses the gap at the frog point. The wing rails and the point define an X-shaped pair of grooves or flangeways. The flangeway is a channel that allows the wheel flange of the car to pass. The flangeway allows the wheel flange to maintain continuous contact with the inner surfaces of the frog through the intersection of the rails.
In order to properly guide a passing car over the frog, a guard-rail is typically placed on the opposite rail. A short rail is placed inside of and parallel to the stock rail opposite the point that the wheels pass through the frog.
The width of the frog is called its spread. Different sized frogs are used for rails making various angled turns. Frogs are generally identified by a frog number, which corresponds to the ratio of the length to the sum of heel and toe spreads. Conventional frogs have standard dimensions according to the frog number. Larger numbered frogs are generally used for larger turn radii.
The mining industry presents challenges for rail crossings. Modern mining cars are longer than their predecessors are. Most mine car wheels are fixed and do not turn. Due to the tight curves in the rails in mining operations, the wheels of these longer rail cars cannot follow the turns easily and easily derail when passing through a frog. As the leading wheels of the car move through the frog to the secondary rail, the car is turned in a different direction from that of the original rail. The fixed rear wheels of the car are pushed to the outside of the turn. In an existing frog, the rear wheel may jump the frog and derail the car. Where cars derail, damage may occur to the car and or the load in the car and the impact of the train car wheels on the frog generates early failure of the crossing.
Wing rails and guard rails have been used in an attempt to prevent derailing; however, no frog exists that adequately prevents derailing of longer fixed-wheel cars, such as those used in mines. A need exists for a frog having the ability to maintain the rear wheels of a car and successfully transfer the car through a turnout or crossover on a track. A need exists for a frog with a flangeway having an adequate width and angle to allow the wheel of a train car riding the wing rail across the intersection to stay in contact with the frog until it is supported by the secondary rail.